Bcl-2 bioactive metabolites produced by Xenorhabdus and Photorhabdus have been isolated and identified and their structure elucidated. These include nematophins, xenorhabdins, xenocoumacins and anthraquinones, xenortides and xenematide, nematophin and peptides. The diversity of the metabolites produced by these bacteria suggests that these metabolites are potential sources of new agrochemical and antimicrobial drugs. In the course of studies on EPN, a new EPN belonging to the genus Rhabditis and subgenus Oscheius was isolated from sweet potato weevil grubs collected from CentralTuber Crops Research Institute farm, Thiruvananthapuram. A specific JAK signaling pathway bacterium was found associated with the nematodes. The nematodes could be cultured on laboratory reared Galleria mellonella larvae and maintained alive for several years. The bacteria were found to be pathogenic to a number of insect pests and could be isolated from third stage infective juveniles of the nematode, from the haemolymph of nematode infested G. mellonella larvae. Based on the sequence of the 16S rDNA and Blast analysis, the bacterium resembles Bacillus cereus isolate 03BB102.
The bacterium has been deposited in IMTECH and the accession number is MTCC 5234. The cell free culture filtrate of the bacteria was found to inhibit survivin several pathogenic bacteria, fungi and a plant parasitic nematode, suggesting that it could be a rich source of biologically active compounds. In this paper, we report the isolation, structure elucidation and antimicrobial activity of two stilbene compounds from the above bacterium. Materials and Methods Chemicals All chemicals used for extraction and purification were of AR grade. High performance liquid chromatography was performed using HPLC grade methanol from Merck, Mumbai, India. Thin layer chromatography was performed using precoated silica gel 60 GF254 plates and column chromatography doxorubicin using silica gel purchased from Merck, Germany. Test micro organisms Gram positive bacteria: Bacillus subtilis MTCC 2756, Staphylococcus aureus MTCC 902, Gram negative bacteria: Escherichia coli MTCC 2622 and Pseudomonas aeruginosa MTCC 2642, medically important fungi: Aspergillus flavus MTCC 183 and Candida albicans MTCC 277, and agriculturally important fungi: Fusarium oxysporum MTCC 284, Rhizoctonia solani MTCC 4634 and Penicillium expansum MTCC 2006.
All the test micro organisms were purchased from Microbial Type Culture collection Centre, IMTECH, Chandigarh, India. Extraction and purification of bioactive compounds A pure culture of the bacterium was obtained from infected G. mellonella larvae and or third stage infective transport juveniles of the nematode isolate and bacterial fermentation was carried out using Tryptic soya broth. Aliquots of the stock culture were added separately into 100 ml sterile medium. The flasks were incubated in a gyrorotatory shaker at 30C in dark for 24 h. When the optical density of the culture at 600 nm was approximately 17, the bacterial cultures were transferred aseptically into 400 ml sterile medium and incubated in the gyrorotatory shaker at 30C in dark for 96 h. The culture media were then centrifuged followed by filtration through a 045 lm filter, to obtain cell free culture filtrate. Thirty litres of cell free culture filtrate were neutralized with co